In certain engine applications it may be desirable to develop a flexible fuel delivery system that provides for a greater range of achievable fuel flow rates through the fuel injector. This range, referred to as the dynamic range, is defined as the ratio between the maximum and the minimum controllable fuel flow rates. In a pulse-width-modulated fuel injector, the fuel flow is not actually controllable at the upper and lower bounds of the injector flow range due to physical constraints. For example, a fuel injector will not open if the pulse delivered to the injector is shorter than the time required for the injector solenoid to energize and open the injector valve. Likewise, a fuel injector will not close if the time between pulses is shorter than the time required for the fuel injector solenoid to deenergize and close the injector valve. These physical conditions limit the dynamic range by bounding the minimum and maximum controllable flow rates.
The fuel flow rate through an injector is directly affected by two factors, fuel pressure and the time an injector is open. The flow rate may be modified by adjusting the open injector time while maintaining a substantially constant fuel pressure. Flow rate may also be varied by altering the fuel pressure with the fuel pump speed. This method requires an extensive electronic control system, specialized hardware, and a relatively expensive fuel pump.